1. Field of the Invention
This invention relates to a recording apparatus, and more particularly to a so-called serial type recording apparatus in which recording means is movable along a recording medium (such as plain paper, worked paper or an OHP sheet) on which recording is to be effected.
The term "recording apparatus" used herein covers an electronic desk top calculator, an electronic typewriter, a facsimile apparatus, a copying apparatus and a printer. The term "recording means" covers recording means using the thermal recording system such as the thermosensitive system or the heat transfer system, recording means using the ink jet recording system such as the bubble jet syste, and recording means using the impact recording system such as the daisy wheel system or the wire dot system.
2. Related Background Art
A recording apparatus in which the reciprocal movement of a carriage and the conveyance of recording paper are accomplished by a single drive source is known. The applicant has previously invented a particularly excellent recording apparatus in which the conveyance of a recording medium and the reciprocal movement of recording means can be accomplished by the use of a reversible drive source. The applicant filed an application for said invention (U.S. application Ser. No. 395,519 filed on Aug. 18, 1989). The invention of the present application which will hereinafter be described as a further development of the aforedescribed recording apparatus. Description will now be made of the background art on which the invention of the present application has been made.
In the recording apparatus as previously described herein the driving of a carriage and the feeding of paper are accomplished by a single drive source, a belt-driving pulley 125 first starts to rotate in the direction of arrow A from the state shown in FIG. 1A of the accompanying drawings. A belt 106 then starts to be moved by the mutual friction between an untoothed portion 106A and the driving pulley 125. Thereafter, the toothed portion 106C of the timing belt 106 and the driving pulley 125 come into meshing engagement with each other. At this time, however, the leading tooth 125a of the driving pulley 125 and the tooth 106C of the timing belt 106 are not synchronized with each other. Therefore, there is the possibility that the rest of the toothed portion 106C of the belt may run on the crest of the teeth of the driving pulley 125 (FIG. 1B of the accompanying drawings).
That is, normally, the crest of the tooth of the driving pulley must come into the valley of the toothed portion of the belt, but there is the possibility that there is brought about an abnormal state in which the crest of one tooth runs on the crest of the other tooth as previously described. If the driving pulley continues to rotate in such an abnormal state, the belt will move while remaining in such an abnormal state. This state is an unstable state, in which the feeding of the belt becomes inaccurate and in addition, normal meshing engagement may be suddenly restored (the crests which run on each other may fall into the valleys).
Such a phenomenon has been confirmed by an experiment as well.
FIG. 1C of the accompanying drawings is a graph showing an example of the above-described phenomenon. It shows that with the belt tension being set to 150 gf and with the feeding speed of the belt-driving pulley being set to 130 mm/sec., when the feeding amount of the belt-driving pulley (from the meshing start point with the toothed portion of the belt) is e.g. 2 mm, the crest of the tooth of the belt-driving pulley and the crest of the toothed portion of the belt run on each other with a probability of about 15%.
The run-on state described above may last even to the printing area and may cause unsatisfactory recording attributable to the impossibility of normal carriage feeding being obtained.